The times. (Owosso, Mich.) 1882-1897, 1887-06-03
IRON GENERALIZATION.
Il Causes Changes I'm the Fiber OF Metal
aud Wealxens II.

Drltlsn ItilWdy piuuScu from INC
great bridge over the Firth of Tay
into the dark waters below, one stormy
December night seven years ago, car
rying every living soul upon it to GER
tain death, there has been no railroad
bridge disaster that has excited so
much public attention as that which
recently occurred on the Boston and
Providence railroad at the Bussey
bridge near Boston. In both the cause
appears to have been structural de-
feet. This may also be said of the
Ashtabula accident, whose horrors,
however, were increased by the fierce
work of the flames and the inclemen-
cies of bitterly cold winter night.
Bridge accidents are considered by
all railroad men as incomparably the
worst to which travel by rail is ex-
posed, and as among the most ditlicwlt
to guard against absolutely. One
source of danger was shown when the
peculiar effects of a locomotives ham,
mer-blows upon a track were eX-
planned. The theory was advanced
that girder of the bridge had broken
beneath the engines drivers, whose
pounding upon the defectively-con-
structed bridge was thus primarily the
cause of the accident. This brings up
phase of railroad and bridge acct
dents which is at present receiving u
great deal of attention. Crystalliza-
ton in the material of iron bridges is
an element of danger now so well
recognized that the Pennsylvania
Railroad company has adopted the
definite policy of substituting stone for
iron bridges, and the same plan is
being followed by other railroad COM
panies.
The lifetime of an iron bridge is
from twenty to twenty-five years, and
constant care is necessary to insure
its safety. The Ashtabula bridge was
thirteen years old, and at the time it
fell beneath the weight of two engines
and heavy express train the theory
was commonly advanced that crystal
lization had impaired its original
strength. The two great moving
causes of Capitalization are vibration
and the hammer blows of the loco
motive, which gradually, by repeated
impact, turn the fibre of the iron or
steel into mass of crystals, needing
only some unusual pressure or blow
to cause them to break apart. Add to
this the oscillation caused by the pas
sage of trains at a high rate of speed,
and it will be seen that an iron bridge
is exposed to peculiar perils, which can
only be guarded against by rigid in
spection and constant renewals.
Capitalization was one of the seve-
raj theories advanced by Park Ben
jamin, New York engineer, to ac-
count for the Tay bridge accident. He
said:
General indications. go to show
that the cause must be sought in an
abnormal condition of the Structure,
or rather one which did not enter into
the calculation of the builders. Such
a condition would be the deterioration
of the metal by its change from
fibrous to a crystalline state under re-
peated vibration. That this occurs in
railway bridges has been vigorously
disputed by many well-known engi-
neers. On the other hand, many ex-
amples are quoted by different authori-
ties to support the theory. Apropos
to this particular accident, q .,distin-
guished French engineer and iron
founder now in this country Informs
us that he has known bars of iron
made by himself from Scotch pig to
change from tough gibrous to
brittle crystalline structure in travel
ing by rail only from the north Of
France to Paris. This is, of course,
an extreme Instance. w ~ " ~
Again, recent research has demon
.sstrated that because structure with
stands large quiescent load that fact
is little proof of stability under re-
peated shocks and vibrations. Metals
ave believed to have life. . 4Abar, fol-
example, may stand "a million vibra-
tons and break down at the million
and first, and yet the last shock may
be lighter than preceding ones. At
tempts, however, to reduce this law to
practical application have elected an
abundance of conflicting evidence; but,
nevertheless, it is well settled that in
no department of mechanics is an ex-
perimenting more urgently needed or
of graver public Importance" r'@
The strength of the Tay bridge at
the time of its building was such that
twas pronounced perhaps the most
remarkable structure in the world"
Engineering,k q British magazine,
speaking of its test, when five engines,
weighing $50 tons, were placed on a
single span, said:
"The result is the complete estab-
lishment of this fact ESQ important to
the public), that the bridge Is strong
out of all proportion to its possible ne
cessities. The load which the struc-
ture is calculated to carry is six times
greater than that to which it was sub
jected."
And yet this great bridge, which
cost 81 10000, collapsed within few
months after it was finished, the acci-
dent being the only one in all railroad
history in whichkno survivor lived to
The theory Of equalization put
forward at the time of the Ashtabula
bridge disaster is now accepted as ac-
counting for many railroad accidents,
and seems peculiarly applicable to the
fall of the Bussey bridge. Vibrations
and hammer blows would seem to have
crystallized some portion of the struc-